The packaging industry makes extensive use of paperboard consisting of two plies of card connected by an intermediate corrugated paperboard layer. This structure relies upon adhesion of the glue between the paper surfaces and needs moisture resistant finishes if deterioration by moisture penetration is to be avoided. This disadvantage applies to all cellulose-based products.
Large volumes of goods are shipped in cartons made from erected rectangular paperboard blanks made from sheet material as described above. For many products such as furniture and white goods, some cushioning is very useful. The only common double skin plastic sheet is CORFLUTE™ board. This resists flexure In all directions but finds limited use in packaging, even though it is capable of taking print and its main use is signage.
DE 101 64057 describes a multi-layered packaging material, one form of which has a top and bottom polyethylene plies mutually connected by a core of side by side foam plastic pipes with inside diameters of 40-60 mm and wall thickness from 10-20 mm. The pipes are made from polyethylene or polystyrene. The pipes are welded to the plies. The material is intended to absorb shock loads.
EP 1369353 describes a laminated packaging material consisting of a top and bottom extruded plastic fluted plies with a core made of multiple superimposed corrugated plies made of fibreboard. Multiple ply products tend to produce extra rigidity, but this is not always an advantage in that cartons tend to be made from folded blanks and thick boards must be notched to allow mitred joints at the folds.